1. Field of the Invention
The present invention relates to conveyor systems and conveyor belts. More specifically, the invention relates to an improved conveyor belt overlay element design for use in conveyor belts that effectively maneuver a curve or a turn and can be used in conveyor systems such as a turn conveyor and a spiral conveyor.
2. Description of Related Art
Conveyor systems are commonly used in various industrial fields for material handling and processing purposes. Many of these conveyor systems are used in harsh environmental conditions with space limitations and high capacity requirements. In such applications, wire conveyor belts are commonly used because of their durability and capacity. These wire conveyor belts are generally assembled from a plurality of overlay elements interlinked together which act to support objects being conveyed.
In one type of wire conveyor belt, the overlay elements are manufactured from wire spirals which are intermeshed and linked together by connecting rods extending transversely across the width of the conveyor belt. Connective links may be provided at the ends of the rods to serve as tractive links which may be driven by a motorized sprocket wheel for the operation of the conveyor belt. An example of such a wire conveyor belt with a wire mesh overlay made from wire spirals is shown in U.S. Pat. No. 4,957,597 to Irwin and U.S. Pat. No. 5,558,208 to Kucharski. As one skilled in the art will recognize, the loops formed by the wire spirals can be circular, elliptical, rectangular, triangular or any other geometrical shape when viewed transversely across the width of the conveyor belt. The selection of the shape of the wire spirals can be based on the objects to be supported and conveyed by the conveyor belt.
In another type of wire conveyor belt, the wire mesh is assembled from overlay elements formed from flat wires that are bent in a zig-zag manner to form a serrated shape. The flat wires are provided with holes or slots placed in various predetermined locations such that the flat wires can be intermeshed and linked together by connecting rods extending transversely across the width of the conveyor belt, much like the mesh overlays formed from wire spirals. An example of such wire conveyor belt with a wire mesh overlay made from flat wires is shown in U.S. Pat. No. 5,141,099 to Baumgartner and U.S. Pat. No. 5,501,319 to Larson et al. Again, one skilled in the art will recognize that the flat wires may be bent in other shapes such as a crank shape disclosed in U.S. Pat. No. 5,501,319 to Larson et al.
These wire conveyor belts have been designed to be partially collapsible in the lateral plane of the belt thereby allowing the belts to turn in a radial path. During a turn, the amount of overlap between the intermeshed overlay elements substantially increases at the inner radial side of the belt or alternatively, the intermeshed overlay elements may expand from an overlapped position at the outer radial side of the belt thereby allowing the wire conveyor belts to effectively maneuver a curve or a turn along the conveyor path. This allows such belts to be used in conveyor systems such as turn conveyors and spiral conveyors. For example, the Kucharski reference clearly shows a conveyor with wire spiral overlay elements where the outer radial side of the belt can expand from an overlapped position. The Baumgartner reference clearly shows a conveyor with intermeshed flat wire overlay elements that allow the conveyor belt to turn in a similar manner.
In utilizing these known belt designs, it has been found that because the amount of overlap between the intermeshed overlay elements substantially increases at the inner radial side of the belt, the overlay elements were frictionally contacting the adjacent, intermeshed overlay elements. This frictional contact causes the overlay elements to wear prematurely and reduces the durability of the belt. In addition, the frictional contact also causes the overlay elements to bind together causing jams in the conveyor system thereby reducing the reliability of the conveyor system.
It has also been found that in a conventional wire conveyor belt, the number of loops at the side of the belt defining the inner radius of the turn far exceeded the number of loops required to effectively support the objects being conveyed. This number of loops required is known as "loop density" and may be defined as the number of loops present in any given constant area on the conveyor belt. Generally in the art, the transverse rods of the wire conveyor belts support the objects being conveyed while the intermeshed overlay elements form the support surface ofthe belt which prevents the objects from falling between the transverse rods. The number of loops formed on the wire spiral is largely dependent upon the width of the belt and the size of the objects being conveyed. The smaller the object being conveyed, the greater the number of loops required (i.e. higher loop density) to prevent the objects from falling between the transverse rods. Thus, the loop density must be high enough to ensure that the objects being conveyed are fully supported and to ensure that the objects do not fall between the transverse rods. However, as noted in the previous discussion, in a conventional wire conveyor belt, the loop density increases dramatically during a turn at the side of the belt defining the inner radius of the turn because of the significant increase in the overlap between the loops. Thus, during a turn, excess loop density exists in conventional belts which is far above the loop density required to ensure that the objects being conveyed do not fall between the transverse rods.
In this regard, because the overlay elements are generally manufactured from heavy materials such as stainless steel, the excess loop density present in conventional belts also signify excess weight of the belt which decreases the durability of the belt. More specifically, the weight of the belt has been found to exert greater forces in welds and in associated structural members, such as tractive links, which are joined to the conveyor belt. This, of course, can cause these welds and associated structural members to fail, thereby decreasing the durability of the belt and the reliability of the conveyor system. Moreover, the heavy weight of the conventional belt diminishes the load capacity of the conveyor system. Since the conveyor drive system has a fixed load capacity, the total weight of the objects being conveyed is correspondingly limited by the heavy weight of the conveyor belt itself. Thus, if the weight of the belt can be effectively reduced, the total weight of the objects being conveyed can be increased by a corresponding amount. The heavy conveyor belt can also cause the conveyor drive system to be over worked which can cause the drive system to fail thereby reducing the reliability of the conveyor system.
Furthermore, the aforementioned excess loop density has been found to decrease the performance of various processing systems that utilize conventional conveyor belts. One example of such processing is in the food industry where convective heat transfer and/or fluids are used to process the food objects being conveyed. For instance, spiral conveyor systems are often used in refrigeration systems such that a food item enters the spiral conveyor and is blasted with cold air flowing through the wire mesh conveyor so that by the time it exits the spiral conveyor, the food item is frozen solid. It has been found that if a conventional, constant pitch wire conveyor belt is used, the increased loop density at the inner side of the belt interferes with the air flow to and around the food item thereby interfering with the effectiveness of the refrigeration system. This results in a non-uniform performance of the refrigeration system since the freezing of the food items is partially dependent upon the food item's position on the belt. Of course, although a specific example of the refrigeration system was discussed, this problem is similarly present in other food processing applications such as baking and cooking conveyor systems where convected heat is used to cook the food item being conveyed. Moreover, this non-uniformity problem exists in other processing applications which are used in a broad range of industries. For example, wash conveyor systems and chemical treatment conveyor systems experience similar non-uniformity problems because the flow of any liquid or gaseous medium through the conveyor belt is not constant across the width of the belt during a turn due to the increased loop density.
It has also been found that the size of the inner turning radius of the conveyor belt is partially limited by the design of the overlay elements. In the context of wire conveyor belts with wire spiral overlay elements, the size of the loops formed by the wire spirals have been found to limit the turning radius because the amount of overlap between the loops substantially increases during the turn. If the loops are large, they restrict the amount of overlap since the loops are at slightly different angles with respect to one another during the turn, thereby limiting the amount of overlap. In a similar manner, if the bends in the overlays formed by flat wires are made such that the bent portions are large, they can restrict the turning radius of the conveyor belt and cause binding if the radius is too small.
One approach to address the above minimum turn radius limitation is to use different overlay elements with different sized loops. According to this belt design, overlay elements with smaller sized loops are used on the side of the belt defining the inner radius of the turn and overlay elements with larger sized loops are used on the side of the belt defining the outer radius of the turn. This approach is exemplified in Baumgartner disclosing the use of two different overlay elements in the wire mesh overlay, each of the two overlay elements having different sized loops. Another approach is exemplified in U.S. Pat. No. 5,558,208 to Kucharski which discloses a conveyor belt design with a wire mesh overlay wherein the wire spirals are tapered so that the loops formed by the wire spirals are smaller toward the side of the conveyor belt defining the inner radius of the turn and the loops are progressively larger toward the side of the conveyor belt defining the outer radius of the turn. Such tapering of the wire spirals in the wire mesh overlay has been found to be effective in reducing the turning diameter of the conveyor belt.
While these wire conveyor belts are effective, especially in turn conveyor and spiral conveyor systems, the conventional overlay elements used in these conveyor belts still frictionally contact and rub against the adjacent overlay elements, especially at the side of belt defining the inner radius of the turn. As discussed previously, this frictional contact causes accelerated wearing and binding of these overlay elements which both decrease the durability of the belt and the reliability of the conveyor system. In addition, most of these designs still fail to effectively minimize the excess loop density and the resulting non-uniform performance of processing systems. Furthermore, new applications of compact conveyor systems have required conveyor belts with an even smaller turn radius which is not possible with the prior art belts.
Lastly, it has also been found that these wire conveyor belts are expensive to manufacture and operate. The materials used to manufacture the overlay elements, such as stainless steel, are very expensive and heavy. The heavy weight of a conventional belt diminishes the load capacity of the conveyor system and, as previously noted, exert greater forces on the various associated structural members of the conveyor belt. Consequently, the drive system operating a conventional wire mesh belt is required to have a higher drive capacity in order to operate with a predetermined load capacity. Furthermore, the conventional belts require various associated structural members of the conveyor belt and the conveyor system, such as the connective links, to be very robust in order for the belt to be durable. Of course, both of these requirements increase the cost of the conveyor system.
Therefore, there exists a need for a conveyor belt with an overlay element design that increases the durability of the belt and the reliability of the conveyor system while minimizing excess loop density and improving the performance of processing systems that utilize such a conveyor. There also exists a need for such a conveyor that decreases the minimum turn radius of the belt while minimizing the cost of the belt and the system requirements of the conveyor system.